Cryogenic systems have also long been utilized in the storage and transporting of specimens including human and animal body fluids such as semen. Such systems commonly employ a cryogenic dewar to store and/or transport the specimens. Such a system, as shown in FIG. 1, comprises a cryogenic dewar that typically includes an inner vessel and an outer casing, each having a central opening at their tops, and a neck portion providing a gas-tight interconnection between the openings of the inner vessel and the outer casing at their tops, thereby forming an evacuable space between the inner vessel and outer casing. One or more sample or specimen holders are provided, each with an elongated support with a hook at its distal end to engage the top of the dewar to suspend the holder within the interior of the inner vessel. The sample holders are typically immersed in a bath of a liquid cryogen, commonly nitrogen, maintained in the inner vessel. The bottom of the inner vessel is provided with means, such as a spider-like device, to maintain the spacing of the specimen holders within the inner vessel to prevent their mutual interference upon insertion and removal. The central opening of the dewar is typically closed or fitted with a foam plug.
When a cryogenic dewar fails to maintain cold temperatures during shipping and storage, the samples or specimens being carried therein can very easily be adversely affected, or even destroyed. To extend the sample holding, in the event the cryogenic dewar is inadvertently turned on its side or knocked over during transport, cryogenic shipping dewars have long been provided with a body of cryoretentive material, such as calcium silicate, within the inner vessel, most generally in cylindrical form surrounding the sample holders, as shown in FIG. 1. The cryoretentive element absorbs liquid cryogen and retains the liquid cryogen if the dewar is inadvertently turned on its side, preventing loss of refrigerant and of the insulating thermal gradient of the interconnection between the inner vessel and outer casing.
Many cryogenic dewars, however, have not been provided with cryoretentive material within their inner vessels because there was no such practice at the time of their manufacture or they were not intended for shipping samples.
Accordingly, there is a need in the industry for a convenient conversion of cryogenic dewars that have no protective cryoretentive element for shipping, for improved ability to maintain samples at cold temperatures for longer periods of time and for improved sample holders with protection against the loss of liquid cryogen.